ES372349A1 - Anistropic thin ferromagnetic film magnetometer - Google Patents

Abstract

In a thin film fluxgate magnetometer, noise is reduced by using a film in which switching is primarily by coherent rotation. Suitable films may be made by evaporation of 18% Fe-82% Ni alloy in vacuo and heating at a temperature of at least 350 C. As shown in Fig.3, two thin magnetic films 12, 121 are subjected to a D.C. polarizing field in the hard direction by series connected windings 20 and to an alternating pumping field of frequency f in the easy direction by parallel connected oppositely poled windings 14, 141. Detection windings 18, 181, coaxial with windings 14, 141, are similarly poled and connected in series to an amplifier 24 tuned to frequency 2f which is connected via a synchronous detector 26 to an indicator or recorder 28. The films may be flat or may be coated on glass-coated copper wire in which case the polarizing field may be generated by passing a direct current through the wire Fig. 5 (not shown). An A.C. polarizing field may be used, in which case a common coil at an angle of 30 to 60 degrees to the easy axis may be used to generate a field having components in the easy and hard directions. Common pumping and detection windings may be used with filters tuned to f and 2f being connected to the pumping generator 16 and amplifier 24 respectively. The detector 26 may be used to control current in compensating windings (not shown), the current necessary to null the field being measured being an indication of the field strength. Three magnetometers may simultaneously measure three different components of the field.